1. Field of the Invention
The present invention relates to a distance measuring device and, more particularly, to a distance measuring device for a camera which measures the distance to an object to be photographed.
2. Description of Related Art
Conventional distance measuring devices for a camera use photocells comprising divided rows of photocells (silicon photo diode, hereinafter, referred to as "SPD") or one-dimensional position sensitive devices (hereinafter, referred to as "PSD"), or a combination of both SPDs and PSDs.
However, when PSDs are used as photocells, it is difficult to form the PSDs on a chip of an integrated circuit for measuring a distance, which is disadvantageous in terms of the space requirements and increase in manufacturing cost. Further, PSDs are liable to be influenced by external noise and have a low distance resolution. Furthermore, when secondary generated light (hereinafter, referred to as scattered light) is incident on a vicinity of an end portion of the PSDs because light emitted from a chip of a light emitting element is irregularly reflected by a molded package or the like, the accuracy of the distance measurement is further deteriorated.
If the width of the PSD is shortened to improve the resolution of the measured distance, the amount of reflected light from an object positioned a long distance away is small and the photo current which is received from the photocell is further reduced, thereby preventing signal processing from being carried out.
When SPDs are used as photocells, the distance measuring accuracy is deteriorated if the number of photocells is small. On the other hand, if the number of photocells is excessively large, a long period of time is required for measuring a distance, and the cost for manufacturing the distance measuring device is high.
When both PSDs and SPDs are used, control of the distance measuring device becomes complicated and the manufacturing cost increases.